Method of encapsulating organic electroluminescence device and organic electroluminescence device

ABSTRACT

PCT No. PCT/JP95/01764 Sec. 371 Date Mar. 5, 1997 Sec. 102(e) Date Mar. 5, 1997 PCT Filed Sep. 5, 1995 PCT Pub. No. WO96/08122 PCT Pub. Date Mar. 14, 1996A method of encapsulation for an organic EL device, which overcomes the difficulty of conventional methods by fully preventing the growth of dark spots in the organic EL device by providing an inert liquid layer having a dissolved oxygen concentration of 1 ppm or less on the periphery of the organic EL device.

TECHNICAL FIELD

The present invention relates to a method of encapsulating an organicelectroluminescence device ("electroluminescence" to be referred to as"EL" hereinafter) and an encapsulated organic electroluminescence device(to be referred to as "encapsulateded EL device" hereinafter).

TECHNICAL BACKGROUND

An EL device has high visibility owing to self-emission of light, andhas excellent impact resistance owing to a complete solid device. Due tothese characteristics, there have been proposed a variety of inorganicEL devices for which inorganic compounds are adapted as a light-emittingmaterial and a variety of organic EL devices for which organic compoundsare adapted as a light-emitting material. Above all, developments oforganic EL devices are actively underway for obtaining organic ELdevices having higher performance, since the organic EL devices permit adecrease in drive voltage to a great extent as compared with inorganicEL devices.

In the basic constitution of an organic EL device, the organic EL devicehas a structure in which an anode, a light-emitting layer and a cathodeare consecutively laminated, and the above organic EL device is formedon a substrate in many cases. The anode and the cathode may be reversedin position. In some cases, further, a hole-transporting layer isprovided between the anode and the light-emitting layer, and anelectron-injecting layer is provided between the cathode and thelight-emitting layer, for improving the performance. The light-emittinglayer is generally formed of one or a plurality of organiclight-emitting materials, while it is sometimes formed of a mixture ofan organic light-emitting material with a hole-transporting materialand/or an electron-injecting material.

Further, in a pair of electrodes (anode and cathode) constituting theorganic EL device, the electrode positioned on a surface through whichlight comes out is formed of a transparent or semi-transparent film forimproving the light emission efficiency and due to a constitution as asurface light-emitting device. The other electrode (to be sometimesreferred to as "opposite electrode" hereinafter) positioned opposite tothe surface through which light comes out is formed of a specific metalthin film (thin film of metal, alloy or a mixture of metals).

The organic EL device having the above constitution is a current-drivenlight-emitting device, and it is required to apply a high electriccurrent between the anode and the cathode for performing light emission.As a result, the device generates heat when the device is emitted, andwhen the device has oxygen or water around it, the oxygen and the waterpromote the oxidation of materials forming the device to degrade thedevice. In the typical degradation of the device by the oxidation andwater, a dark spot occurs and grows. The dark spot refers to a faultpoint of light emission. As the oxidation of the materials forming thedevice proceeds with the driving of the organic EL device, the existingdark spot grows, and eventually, the dark spot spreads over the entiretyof the light-emitting surface.

For preventing the above degradation, a variety of methods have beenhitherto proposed. For example, for effectively removing heat which thedevice generates when the device is emitted, JP-A-4-363890 discloses amethod in which an organic EL device is held in an inert liquid compoundof liquid fluorinated carbon. As a method of removing water which is oneof those which cause the degradation, JP-A-5-41281 discloses a method inwhich an organic EL device is held in an inert liquid compound preparedby incorporating a dehydrating agent such as synthetic zeolite intoliquid fluorinated carbon (specifically, the same as the liquidfluorinated carbon disclosed in the above JP-A-4-363890). Further,JP-A-5-114486 discloses a method in which a heat-radiating layerencapsulating a fluorocarbon oil (specifically, included in the liquidfluorinated carbon disclosed in the above JP-A-4-363890) is formed on atleast one of the anode and the cathode and heat generated at a time ofdriving the device is radiated through the heat-radiating layer toextend the light emission life of the device.

The degradation caused by water takes place in an inorganic EL device aswell. As a method of preventing the degradation of the inorganic ELdevice, there is a method in which an inorganic EL device isencapsulated between a pair of glass substrates while providing apredetermined space and the space is charged with a protective liquid.U.S. Pat. No. 4,446,399 discloses a method in which silicone oil orsilicone grease is used as the above protective liquid. U.S. Pat. No.4,810,931 discloses a method in which a liquid obtained by degassing aperfluorinated inert liquid (specifically, the same as, or similar to,the liquid fluorinated carbon disclosed in the above JP-A-4-363890)under conditions of a liquid temperature of approximately 90 to 120° C.and an ambient pressure of about 10 Torr is used as the above protectiveliquid.

However, the occurrence and the growth of a dark spot in an organic ELdevice cannot be fully prevented even if the above conventional methodson the organic EL device are relied upon. The reason therefor is assumedto be as follows.

For preventing the occurrence and the growth of the dark spot, it is oneof useful means to utilize liquid fluorinated carbon for removing theheat which the organic EL device generates when the device is emitted orto use a dehydrating agent for removing water which infiltrates theorganic EL device during or after the organic EL device is encapsulated.However, studies by the present inventors show that the liquidfluorinated carbon and the fluorocarbon oil greatly dissolve gases, andnot water which externally infiltrates but oxygen dissolved in theliquid fluorinated carbon or the fluorocarbon oil has a great influenceon the occurrence and the growth of the dark spot. For example,perfluoroamine (Fluorinert (trade name), supplied by Sumitomo-3M Co.,Ltd.) contains dissolved air in a maximum amount of 22 milliliters per100 milliliters thereof (dissolved oxygen concentration 63 ppm). It istherefore difficult to fully prevent the occurrence and the growth ofthe dark spot by the above-described conventional methods on the organicEL device.

On the other hand, when the method of using a silicone oil or siliconegrease as a protective liquid, among the above conventional methods onan inorganic EL device, is applied to the organic EL device, there iscaused a problem that the organic EL device is degraded or broken by thesilicone oil or the silicone grease. Further, when the method of using,as a protective liquid, a perfluorinated inert liquid which is degassedunder the above-specified conditions is applied, it is difficult tofully prevent the occurrence and the growth of the dark spot in theorganic EL device.

It is an object of the present invention to provide a method ofencapsulating an organic EL device, in which the growth of the dark spotin the organic EL device can be firmly prevented, and an encapsulatedorganic EL device in which the growth of a dark spot is well prevented.

DISCLOSURE OF THE INVENTION

The method of encapsulating an organic EL device in the presentinvention, which achieves the above object, has a characteristic featurein that an inert liquid layer having a dissolved oxygen concentration of1 ppm or less is provided on the periphery of an organic EL deviceformed by laminating an anode and a cathode through at least alight-emitting layer.

Further, the encapsulated organic EL device of the present invention,which achieves the above object, has a characteristic feature in thatthe encapsulated organic EL device has an organic EL device and an inertliquid layer which is provided on the periphery of the organic EL deviceand has a dissolved oxygen concentration of 1 ppm or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross sectional view of an encapsulated organic ELdevice obtained in Example 1.

FIG. 2 is a schematic cross sectional view of an encapsulated organic ELdevice obtained in Example 3.

PREFERRED EMBODIMENTS OF THE INVENTION

First, the method of encapsulating an organic EL device in the presentinvention will be explained. In this method, an inert liquid layerhaving a dissolved oxygen concentration of 1 ppm or less is provided onthe periphery of an organic EL device as described above. The reason forthe limitation of the above dissolved oxygen concentration of the inertliquid layer to 1 ppm or less is that it is difficult to firmly preventthe growth of a dark spot when the dissolved oxygen concentration of theinert liquid layer exceeds 1 ppm. The lower the dissolved oxygenconcentration is, the more desired it is. In a practical sense, however,the dissolved oxygen concentration is preferably in the range of from0.01 to 1 ppm, particularly preferably 0.1 ppm or less.

The term "inert liquid" in the present invention refers to a chemicallyand physically stable liquid, and for example, it means a liquid whichhas stability and undergoes neither a chemical reaction nor dissolutionwhen brought into contact with other substance. Specific examples of theinert liquid include liquid fluorinated carbons such asperfluoroalkanes, perfluoroamines and perfluoropolyethers. The liquidfluorinated carbons are particularly suitable inert liquids, since theyhave advantages that (1) they are excellent in electrical insulation(for example, Demnum S-20 shown in Table 1 to be described later shows abreakdown voltage of 72 kV when a sample has a thickness of 2.5 mm),that (2) they have the property of being dissolved in neither water noroil, so that they substantially do not dissolve any layers forming anorganic EL device, and that (3) they have low wettability to the surfaceof a metal and glass so that they substantially do not cause the peelingof an electrode by infiltrating a gap between a substrate surface andthe electrode present directly thereon (electrode constituting anorganic EL device) when the organic EL device is formed on a substrate.

The above liquid fluorinated carbons are commercially available. Since,however, the dissolved oxygen concentration of the inert liquid used inthe present invention is limited to 1 ppm or less and since thecommercially available liquid fluorinated carbons have a dissolvedoxygen concentration of far greater than 1 ppm, they cannot be used inthe method of the present invention as they are. When those inertliquids have a dissolved oxygen concentration of greater than 1 ppm,they are therefore used in the method of the present invention after thedissolved oxygen concentration thereof is decreased to 1 ppm or less bya ordinary temperature vacuum degassing method, a freeze vacuumdegassing method or an inert gas replacement method. The method ofdecreasing the dissolved oxygen concentration is properly selecteddepending upon the kind of the inert liquid to be used.

For example, most of perfluoroalkanes and perfluoroamines have a vaporpressure of over 10⁻² Torr at 25° C. When attempts are made to carry outan ordinary temperature vacuum degassing method with regard to thosehaving a vapor pressure of over 10⁻² Torr at 25° C., the vacuum degreecannot be increased to the vapor pressure or less, ard the evaporationthereof easily proceeds at room temperature, so that it is verydifficult to decrease the dissolved oxygen concentration by the ordinarytemperature vacuum degassing method. With regard to those having a vaporpressure of over 10⁻² Torr at 25° C., it is therefore preferred todecrease the dissolved oxygen concentration by a freeze vacuum degassingmethod or an inert gas replacement method.

When the dissolved oxygen concentration is decreased by a freeze vacuumdegassing method, for example, a series of operations including the stepof freezing a degassing object (inert liquid whose dissolved oxygenconcentration is to be decreased) to be degassed with liquid nitrogen,or the like, the step of vacuuming the degassing object in a frozenstate at 10⁻² Torr or less and the step of melting the degassing objectin a frozen state after the vacuuming are carried out as many times asdesired until the degassing object has a dissolved oxygen concentrationof 1 ppm or less. When the degassing object is selected from FluorinertFC-72, Fluorinert FC-84, Fluorinert FC-77 and Fluorinert FC-75 (all ofthese are trade names and included in perfluoroalkanes) supplied bySumitomo-3M Co., Ltd. and Fluorinert FC-40, Fluorinert FC-43 andFluorinert FC-70 (all of these are trade names and included inperfluoroamines) supplied by the same Company as above, a series of theabove operations are repeated at least five times, whereby an intendedmaterial can be obtained. When the dissolved oxygen concentration isdecreased by an inert gas replacement method, for example, 0.1 to 1liter/minute, per 50 cc of a degassing object, of an inert gas (argongas, nitrogen gas, helium gas, neon gas, or the like) is fed to thedegassing object to cause a bubbling approximately for 4 to 8 hoursuntil the dissolved oxygen concentration of the degassing object is 1ppm or less. Of the above two methods, the free vacuum degassing methodis preferred in that the dissolved oxygen concentration can be decreasedwithin a relatively small period of time.

On the other hand, most of perfluoropolyethers have a vapor pressure of10⁻² Torr or less at 25° C. With regard to those having a vapor pressureof 10⁻² Torr or less at 25° C., the dissolved oxygen concentration canbe decreased by a ordinary temperature vacuum degassing method as wellas by the vacuum freeze degassing method or the ine--t gas replacementmethod since they have a low vapor pressure at room temperature and showa small evaporation amount at room temperature.

When the dissolved oxygen concentration of an inert liquid having avapor pressure of 10⁻² Torr or less at 25° C. is decreased by theordinary temperature vacuum degassing method, for example, a degassingobject held at 160° C. or lower is subjected to vacuuming at 10⁻² Torror less until the dissolved oxygen concentration of the degassing objectis 1 ppm or less. When the degassing object has a kinetic viscosity of65 cSt or less at the time of degassing operation, dissolved oxygen canbe relatively easily degassed. When the degassing object has a highkinetic viscosity at the time of degassing operation, oxygen and waterare firmly stuck among molecules, and sufficient degassing is difficult.It is therefore preferred to decrease the kinetic viscosity of thedegassing object by heating, or the like. In this case, however, thedegassing operation is complicated. At a degassing time, the degassingobject may be stirred and/or a zeolite may be introduced into thedegassing object as required. When the zeolite is used, the zeolite ispreferably selected from those formed of porous materials such as abiscuit, glass and polytetrafluoroethylene (Teflon) . When the intendedobject is obtained by the ordinary temperature vacuum degassing method,the time required for the degassing operation is approximately for 0.1to 2 hours so long as the degassing object has a kinetic viscosity of 65cSt or less at the time of the degassing operation.

Further, when the dissolved oxygen concentration of an inert liquidhaving a vapor pressure of 10⁻² Torr or less at 25° C. is decreased bythe freeze vacuum degassing method or the inert gas replacement method,the degassing is carried out in the same manner as in the proceduresused for an inert liquid having a vapor pressure of over 10⁻² Torr at25° C.

With regard to inert liquids having a vapor pressure of 10⁻² Torr orless at 25° C., the dissolved oxygen concentration is preferablydecreased by the ordinary temperature vacuum degassing method out of theabove three methods, since the dissolved oxygen concentration can bedecreased by the operation for a shorter period of time and since thedegassing operation is simple.

Specific examples of inert liquid, from which inert liquids having adissolved oxygen concentration of 1 ppm or less can be easily obtainedby the ordinary temperature vacuum degassing method include variousperfluoropolyethers as shown in the following Table 1.

                  TABLE 1    ______________________________________                                      Kinetic                           Vapor pressure                                      viscosity    Trade Name  Manufacturer                           (Torr) at 25° C.                                      (cSt) at 25° C.    ______________________________________    Demnum S-20 Daikin     10.sup.-6  53                Industries Ltd.    Fomblin Z03 Montecatini                           10.sup.-4  30    Fomblin M03 Montecatini                           --         30    Fomblin Y04 Montecatini                           --         38    Fomblin Y06 Montecatini                           --         60    Fomblin YLVAC06/06                Montecatini                           10.sup.-6  62    Fomblin Z DEAL                Montecatini                           10.sup.-4  20    Fomblin Z DIAC                Montecatini                           10.sup.-5  60    Galden HT250                Montecatini                           10.sup.-2  10    Galden HT270                Montecatini                           10.sup.-2  20    ______________________________________

Demnum S-20 in the above Table 1 has an average molecular weight of2,700, a breakdown voltage of 72 kV as sample having a thickness of 2.5mm and a volume resistivity of 10¹³ Ωcm at about 20° C. or lower. Thestructural formula thereof is represented by the following formula (1).##STR1## Average molecular weight 2,700

Further, the structural formula of Fomblin Z03 in Table 1 is representedby the following formula (2).

    CF.sub.3 -- (--O--CF.sub.2 --CF.sub.2 --).sub.p --(--O--CF.sub.2 --).sub.q --!--O--CF.sub.3                                          (2)

Average molecular weight 4,000

The structural formula of Galden II250 in Table 1 is represented by thefollowing formula (3). ##STR2## Average molecular weight 1,320

In the method of the present invention, the above inert liquid is usedto form an inert liquid layer having a dissolved oxygen concentration of1 ppm or less on the periphery of an organic EL device. The above inertliquid is particularly preferably an inert liquid of which not only thedissolved oxygen concentration is decreased to 1 ppm or less but alsothe water content is decreased to 10 ppm or less. When the dissolvedoxygen concentration of the inert liquid is decreased to 1 ppm or lessby the ordinary temperature vacuum degassing method, the dissolvedoxygen concentration is decreased to 1 ppm or less by this method and atthe same time, the degassing operation is further repeated, whereby aninert liquid having a dissolved oxygen concentration of 1 ppm or lessand a water content of 10 ppm or less can be obtained. When thedissolved oxygen concentration of the inert liquid is decreased to 1 ppmor less by the inert gas replacement method, the dissolved oxygenconcentration is decreased to 1 ppm or less by this method, and at thesame, the bubbling is carried out for a little longer period of time,whereby an inert liquid having a dissolved oxygen concentration of 1 ppmor less and a water content of 10 ppm or less can be obtained. And, whenthe dissolved oxygen concentration of the inert liquid is decreased to 1ppm or less by the freeze vacuum degassing method, the inert liquid isdistilled under vacuum to obtain a first cut, a main cut and a last cutbefore or after the dissolved oxygen concentration is decreased to 1 ppmor less by this method, and the first cut and the last cut are removed,whereby an inert liquid having a dissolved oxygen concentration of 1 ppmor less and a water content of 10 ppm or less can be obtained. When aninert liquid having a dissolved oxygen concentration of 1 ppm or lessand a water content of 10 ppm or less is used, the growth of a dark spotcan be more firmly prevented.

When the above inert liquid layer is provided on the periphery of anorganic EL device, the organic EL device as a whole may be immersed inthe inert liquid filled in a container to form the inert liquid layer onthe periphery of the above organic EL device. However, when the organicEL device is formed on a substrate, the inert liquid layer is preferablyformed as follows. That is, the inert liquid layer is preferably formedby providing a housing material, which is to cover the organic EL devicein combination with the above substrate while forming a space betweenthe organic EL device and the housing material, outside the organic ELdevice formed on the substrate, and filling the inert liquid in thespace formed by the above substrate and the above housing material. Thefilling of the inert liquid is carried out by injecting the inert liquidinto the space through an inlet which is formed in the housing materialor the substrate in advance, and the above inlet is closed after theinjection of the inert liquid.

In the above case, the above housing material is a cap-shaped,plate-shaped (e.g., counterbored substrate), sheet-shaped or film-shapedmaterial having a concave portion having an inner dimension greater thanthe outer dimension of the organic EL device which is to beencapsulated. The housing material is fixed onto the substrate such thatit forms a substantially closed space in combination with the abovesubstrate. In this case, the organic EL device as an encapsulatingobject is in a state in which it is encased in the above concaveportion. When a plurality of organic EL devices are formed on asubstrate, a plurality of the housing materials may be provided suchthat one housing material corresponds to one organic EL device, or theabove housing material as one common sheet may be provided such that itcorresponds to all of the organic EL devices. Further, a plurality ofthe above housing materials may be provided such that each housingmaterial corresponds to a plurality of the organic EL devices as part ofall of the organic EL devices. Similarly, concerning the above concaveportion formed in the housing material, concave portions may be providedsuch that one concave portion corresponds to one organic EL device, theabove concave portion may be provided such that it has a size sufficientto encase all the organic EL devices, or a plurality of the concaveportions may be provided such that each concave portion can encase aplurality of the organic EL devices as part of all of the organic ELdevices.

The housing material can be fixed onto the substrate with any one ofvarious adhesives such as epoxy-resin-containing adhesives andacrylate-resin-containing adhesives. Specifically, those whichdifficultly permeate water and oxygen are preferable. As examples, thereis ARALDITE AR-R30 (trade name of epoxy resin adhesive, supplied by CibaGeigy) . Further, there are a variety of resins such as thermosettingresins and photo-curable resins which can be used as a substitute forthe above adhesive.

The material of the housing material is preferably an electricallyinsulating substance such as a glass and a polymer. Specific examplesthereof include soda lime glass, borosilicate glass, silicate glass,silica glass, fluorescence-free glass, quartz, an acrylic resin, astyrene resin, a polycarbonate resin, an epoxy resin, polyethylene,polyester and a silicone resin. Further, when the organic EL device asan encapsulating object has insulation-coated lead wires as lead wiresfrom the electrodes or when the housing material is fixed onto thesubstrate with an electrically insulating adhesive or an electricallyinsulating resin, the housing material may be formed of an electricallyconductive material such as stainless steel or aluminum alloy.

When the inert liquid layer is formed by charging the inert liquid intothe space formed between the above substrate on which the organic ELdevice is formed and the above housing material, the inert liquid may beinjected into the above space in the atmosphere, while it is preferredto inject the inert liquid into the above space in a nitrogen gasatmosphere or an argon gas atmosphere for preventing the dissolving ofoxygen and water in the inert Liquid at the time of the injectionoperation. Further, the charging may be carried out by a so-calledvacuum injection method.

The above term "vacuum injection method" refers to a method in which aspace to which a liquid to be injected ("injectant" hereinafter) is tobe injected is maintained in a degassed state and the injectant isinjected to the space in the above state or a method in which the spaceto which the injectant is to be injected is degassed and the injectantis injected into the space by utilizing a difference between thepressure of the space and the pressure of an atmosphere surrounding afeed source of the injectant (the former has a lower pressure) .Specifically, there are the following methods (i) to (iii) below.

(i) An object (the entirety of an object having a space into which theinjectant is to be injected) is immersed in a vessel containing theinjectant, and in this sate, heating and pressure reduction are carriedout to degass the above space and the injectant is injected (seeJP-B-57-47559, column 6, lines 13 to 18).

(ii) A container (feed source of the injectant) containing the injectantand an object (the entirety of an object having a space into which theinjectant is to be injected) are placed in a vacuum chamber, and thepressure in the vacuum chamber is reduced. Then, a flow is formedbetween the above space and the feed source of the injectant with atube, and then the system as a whole is exposed to atmosphere to injectthe injectant into the object by utilizing atmospheric pressure (seeJP-B-57-47559, column 7, lines 15 to 26).

(iii) An object (the entirety of an object having a space into which theinjectant is to be injected) is placed in an uncovered container, thecontainer with the object in it is placed in a vacuum container, and thepressure in the vacuum container is reduced. In this case, the object isplaced such that the injectant inlet provided to the above object ispositioned close to the bottom of the above uncovered container. Then,the injectant is introduced into the above uncovered container fromoutside the above vacuum container, and the injectant is charged intothe container until the above inlet is fully covered with the injectant.Thereafter, dry gas is introduced into the vacuum container to bringback the pressure in the vacuum container to atmospheric pressure, andthe injectant is injected into the above space by utilizing a differencebetween the pressure (atmospheric pressure) of an atmosphere surroundingthe injectant contained in the above container and the pressure in thespace to which the injectant is to be injected (see JP-A-64-57590, page2, left bottom column, line 4 to page 3, left top column, line 9).

When the inert liquid is injected, the inert liquid may be heated toincrease its flowability regardless of its injection methods.

The closing of the inlet after the injection of the injectant ispreferably carried out in an inert gas atmosphere such as nitrogen gasatmosphere or argon gas atmosphere rather than it is carried out in theatmosphere. The inlet can be closed with one of the above adhesives orthe above resins which are described as one used for fixing the housingmaterial to the substrate.

The encapsulating as an object of the present invention can be carriedout by forming an inert liquid layer having a dissolved oxygenconcentration of 1 ppm or less on the periphery of an organic EL deviceas described above. At the same time, the encapsulated organic EL deviceas an object of the present invention can be also obtained. In thiscase, when the above inert liquid layer is formed from the inert liquidcontaining an adsorbent, the encapsulation can be carried out moreeffectively, and there can be obtained an encapsulated organic EL devicewhich is more effectively encapsulated.

The above adsorbent works to prevent the infiltration of oxygen andwater into an organic EL device from outside when or after the organicEL device is encapsulated. The adsorbent is not specially limited solong as it adsorbs oxygen and water, while there is preferred anadsorbent which has the properties of adsorbing them in a large amountand sparingly releasing oxygen and water which are once adsorbed. Theadsorbent is not specially limited in form, while an adsorbent havingthe form of a powder is preferred due to its large adsorption area.

Specific examples of the above adsorbent include

(1) an inorganic compound selected from activated alumina, diatomaceousearth, activated carbon, hemihydrated gypsum, phosphorus pentoxide,magnesium perchlorate, potassium hydroxide, calcium sulfate, calciumbromide, calcium oxide, zinc chloride, zinc bromide or anhydrous coppersulfate,

(2) a metal selected from the metal group consisting of lithium,beryllium, potassium, sodium, magnesium, rubidium, strontium andcalcium,

(3) an alloy of metals selected from the above metal group, and

(4) an acrylic water-absorption polymer or a methacrylicwater-absorption polymer. The above adsorbents may be used alone or incombination of at least two of them.

The adsorbent is preferably used in a state in which it has sufficientcapability of adsorption. For this reason, it is preferred to removeoxygen and water adsorbed to the adsorbent before use (the treatment forremoving oxygen and water adsorbed to the adsorbent will be referred toas "activation treatment" hereinafter). Although differing dependingupon the kind of the adsorbent, the activation treatment of theadsorbent can be carried out by a method in which the adsorbent isheated, the adsorbent is subjected to vacuuming, the adsorbent isallowed to stand in an inert gas current or the surface of the adsorbentis cut and removed or by a method combining at least two of thesemethods.

The activation treatment of the adsorbent is preferably carried outwhile the adsorbent is isolated from the atmosphere. Further, theactivation-treated adsorbent is also preferably kept isolated from theatmosphere until it is used for forming the intended inert liquid layer(layer containing the adsorbent) in order to prevent a decrease in theactivity thereof. For example, preferably, the activation treatment byheating or vacuuming is carried out in a state in which the adsorbent isplaced in a container capable of blocking off the atmosphere, such as acontainer with a vacuum valve, the valve is closed after the activationtreatment is completed, and the activation-treated adsorbent is storedin a state in which the atmosphere is blocked off, until it is used.

The amount of the adsorbent can be selected as required depending uponthe kind of the adsorbent. Generally, the larger the amount of theadsorbent is, the higher the adsorption effect is. However, when theamount of the adsorbent is too large, (a) a mixture prepared by addingthe adsorbent to the above inert liquid may show an extremely decreasedfluidity, so that it is sometimes difficult to form the intended inertliquid layer (layer containing the adsorbent), and (b) the adsorbent maydamage an organic EL device.

When an adsorbent having a small particle diameter is used to preparethe above mixture, the mixture shows a decreased fluidity than a mixturecontaining an adsorbent having the same weight but having a largerparticle diameter, and as a result, it is more difficult to form theintended inert liquid layer (layer containing the adsorbent) . However,the adsorbent having a small particle diameter shows a larger adsorptionamount since it has a larger effective area than the adsorbent having alarge particle diameter. It cannot therefore mean that an encapsulatingeffect is low when the amount (weight) of the adsorbent is small.Although depending upon the kind and the particle diameter of theadsorbent, the amount of the adsorbent is preferably in the range ofapproximately from 1 mg to 10 g per milliliter of the above inertliquid, more preferably in the range of approximately from 30 mg to 3 gper milliliter of the above inert liquid.

The inert liquid used for forming the intended inert liquid layercontaining the adsorbent may be an inert liquid which has a dissolvedoxygen concentration of more than 1 ppm before it contains the adsorbentand which shows a dissolved oxygen concentration of 1 ppm or less afterit contains the adsorbent. For forming the inert liquid layer having ahigher encapsulating effect, however, the inert liquid preferably has adissolved oxygen concentration of 1 ppm or less before it contains theadsorbent. The inert liquid used in the above case is thereforepreferably an inert liquid whose dissolved oxygen concentration isdecreased to 1 ppm or less by the above ordinary temperature vacuumdegassing method, freeze vacuum degassing method or inert gasreplacement method.

When the inert liquid containing the adsorbent is used to form the inertliquid layer on the periphery of an organic EL device, the organic ELdevice as a whole may be immersed in the inert liquid (liquid containingthe adsorbent) filled in a container to form the inert liquid layer onthe periphery of the above organic EL device. However, when the organicEL device is formed on a substrate, the inert liquid layer is preferablyformed by providing a housing material, which is to cover the organic ELdevice in combination with the above substrate while forming a spacebetween the organic EL device and the housing material, outside theorganic EL device formed on the substrate, and filling the inert liquid(liquid containing the adsorbent) in the space formed by the abovesubstrate and the above housing material.

Specific examples of the method of providing the above inert liquidlayer on the periphery of an organic EL device by utilizing a housingmaterial include the following methods (A) and (B).

(A) A method in which the adsorbent and the inert liquid are mixed toprepare a mixture and the mixture is filled in the above space formed bythe substrate on which the organic EL device is formed and the housingmaterial which covers the organic EL device on the substrate, to formthe intended inert liquid layer.

When the inert liquid layer is formed by the above method, the abovemixture should not be prepared in the atmosphere, and it is preferred toprepare the above mixture in a dry inert gas atmosphere (nitrogen gasatmosphere or argon gas atmosphere), for example, in a gloved box inwhich the atmosphere is purged with a dry inert gas. When the mixture isprepared, the inert liquid (liquid containing no adsorbent) may bepoured into a container in which the adsorbent is placed, or theadsorbent may be placed in a container containing the inert liquid(liquid containing no adsorbent) . Further, a container for preparingthe mixture may be prepared in addition to a container containing theadsorbent and a container containing the inert liquid (liquid containingno adsorbent), and the adsorbent and the inert liquid may be placed inthe above container concurrently or separately. When the adsorbent andthe inert liquid are separately placed in the container for preparingthe mixture, any one of them may be placed first.

The intended inert liquid layer can be formed from the above mixture bycharging the mixture into the above space through an inlet provided inadvance in the above substrate on which the organic EL device is formedor the housing material covering the organic EL device on the substrateand closing the outlet after the charging. It is also preferred to formthe inert liquid layer in a dry inert gas atmosphere.

The above method is suitable for forming the inert liquid layer from themixture (inert liquid containing the adsorbent) having a high fluidity.

(B) A method in which the adsorbent and the inert liquid are separatelycharged into the above space formed by the substrate on which theorganic EL device is formed and the housing material covering theorganic EL device on the substrate, to form the intended inert liquidlayer.

The above method can be further classified into the following threemethods (b1) to (b3). In any one of these methods, it is preferred toform the inert liquid layer in an inert gas atmosphere.

(b1) The adsorbent is placed in a region within the above space on theorganic EL device and on the substrate on which the organic EL device isformed, then, the housing material is provided on the substrate, and theinert liquid (liquid containing no adsorbent) is charged into the abovespace through an inlet provided in the above substrate or the abovehousing material in advance, thereby to form the intended inert liquidlayer. The inlet is closed after the inert liquid (containing noadsorbent) is charged.

(b2) The adsorbent is placed in a concave portion which is present inthe housing material and concerned in forming the above space, thehousing material is provided on the substrate on which the organic ELdevice is formed, and then the inert liquid (liquid containing noadsorbent) is charged into the above space through an inlet provided inthe above substrate or the above housing material in advance, thereby toform the intended inert liquid layer. The inlet is closed after theinert liquid (containing no adsorbent) is charged.

(b3) The housing material is provided on the substrate on which theorganic EL device is formed, and the adsorbent and the inert liquid arecharged into the above space through an inlet provided in the abovesubstrate or the above housing material in advance one after the other,thereby to form the intended inert liquid layer. The inlet is closedafter the adsorbent and the inert liquid (containing no adsorbent) arecharged.

The organic EL device as an encapsulating object in the method of thepresent invention will be explained hereinafter.

The device constitution of the organic EL device as an encapsulatingobject in the present invention is not specially limited, and the objectcan include organic EL devices having various device constitutions. Theconstitution of the organic EL device in the present invention includesvarious device constitutions.

Specific examples of layer structure of the organic EL device in whichlight comes out through the substrate side include the following (1) to(4) as to the lamination order on the substrate surface.

(1) Anode/light-emitting layer/cathode

(2) Anode/light-emitting layer/electron-injecting layer/cathode

(3) Anode/hole-transporting layer/light-emitting layer/cathode

(4) Anode/hole-transporting layer/light-emittinglayer/electron-injecting layer/cathode

The above light-emitting layer is formed of one or a plurality oforganic light-emitting materials, while it is sometimes formed of amixture of an organic light-emitting material with a hole-transportingmaterial and/or an electron-injecting material. In some cases, further,a protective layer is formed on the periphery of a device having theabove layer structure to cover the device, for preventing theinfiltration of water into the device.

The above organic EL device is generally formed by consecutively formingeach layer including the anode and the cathode on a substrate, while thesubstrate is not used in some cases. When the substrate side is asurface through which light comes out (light-emitting surface) in anorganic EL device formed on a substrate, the layers are consecutivelylaminated such that the anode is present immediately on the substrate.In this case, the substrate is formed of a substance which has a hightransmittance (about 80% or more) to light emitted from the organic ELdevice (EL light), and specifically, it is selected from a plate-shapedsubstrate, a sheet-shaped substrate or a film-shaped substrate formed oftransparent glass, transparent plastic or quartz.

As materials for the anode, the cathode, the light-emitting layer, thehole-transporting layer, electron-injecting layer and the protectivelayer, a variety of materials can be used for each. For example, theanode material is preferably selected from metals, alloys orelectrically conductive compounds having a high work function (e.g., atleast 4 eV) or mixtures of these. Specific examples thereof includemetals such as gold and nickel and electrically conductive materialssuch as CuI, ITO, SnO₂ and ZnO. Although depending upon materials, thethickness of the anode can be generally set in the range of from 10 nmto 1 μm as required.

Further, the cathode material is preferably selected from metals, alloysor electrically conductive compounds having a low work function (e.g., 4eV or less) or mixtures of these. Specific examples thereof includesodium, sodium-potassium alloy, magnesium, lithium, alloy and mixture ofmagnesium with silver, aluminum, Al/Al₂ O₃, indium, and rare earthmetals such as ytterbium. Although depending upon materials, thethickness of the cathode can be generally set in the range of from 10 nmto 1 μm as required.

In each of the anode and the cathode, the sheet resistance is preferablyseveral hundreds Ω/□ or less. The size of the work function used as thestandard for electing the anode material and the cathode material shallnot be limited to 4 eV.

The material for the light-emitting layer (organic light-emittingmaterial) can be selected from those which can form a light-emittinglayer of an organic EL device, i.e., a layer having injection functionsof being able to receive holes injected from the anode or thehole--transporting layer and at the same time being able to receiveelectrons injected from the cathode or the electron-injecting layer whenan electric field is applied, transportation functions of movinginjected charges (at least electrons or holes) under the force of anelectric field, and light emission functions of providing a site whereelectrons and holes are recombined to emit light. Specific examplesthereof include benzothiazole-, benzoimidazole- andbenzooxazole-containing fluorescent whiteners, a metal chelated oxinoidcompound, a stylylbenzene-containing compound, a distyrylpyrazinederivative, a polyphenyl-containing compound, 12-phthaloperinone,1,4-diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene, anaphthalimide derivative, a perylene derivative, an oxadiazolederivative, an aldazine derivative, a pyrazoline derivative, acyclopentadiene derivative, a pyrrolopyrrole, derivative, a styrylaminederivative, a coumarine-containing compound, an aromatic dimethylidenecompound and a metal complex of 8-quinolinol derivative. Although notspecially limited, the thickness of the light-emitting layer isgenerally set in the range of from 5 nm to 5 μm as required.

The material for the hole-transporting layer (hole-transportingmaterial) may be any material so long as it has one of the capability oftransporting holes and the property of being barriers against electrons.Specific examples thereof include a triazole derivative, an oxadiazolederivative, an imidazole derivative, a polyarylalkane derivative, apyrazoline derivative, a pyrazolone derivative, a phenylenediaminederivative, an arylamine derivative, an amino-substituted chalconederivative, an oxazole derivative, styrylanthracene derivative,afluorenone derivative, a hydrazone derivative, a stilbene derivative, asilazane derivative, a polysilane-containing compound, ananiline-containing compound, electrically conductive oligomers having ahigh molecular weight such as a thiophene oligomer, a porphyrincompound, an aromatic tertiary amine compound, a styrylamine compoundand an aromatic dimethylidene-containing compound. The thickness of thehole-transporting layer is not specially limited, either, while it isgenerally set in the range of 5 nm to 5 μm as required. Thehole-transporting layer may have the structure of a monolayer formed ofone or at least two of the above materials, or it may have the structureof a plurality of layers each of which is formed of the same material ordifferent materials.

The electron-injecting layer may be any layer so long as it has thefunction of transferring electrons injected from the cathode to thelight-emitting layer. Specific examples of the material therefor(electron-injecting maternal) include heterocyclic tetracarboxylic acidanhydrides such as a nitro-substituted fluorenone derivative, ananthraquinodimethane derivative, a diphenylquinone derivative, athiopyran dioxide derivative and a naphthaleneperylene, carbodiimide, afluorenylidenemethane derivative, an anthraquinodimethane derivative, ananthrone derivative, an oxadiazole derivative, a metal complex of8-quinolinol derivative, metal-free phthalocyanine, metalphthalocyanine, compounds formed by replacing the terminal of thesecompounds with an alkyl group or a sulfone group, and a distyrylpyrazinederivative. The thickness of the electron-injecting layer is notspecially limited, either, while it is generally set in the range offrom 5 nm to 5 μm as required. The electron-injecting layer may have thestructure of a monolayer formed of one or at least two of the abovematerials, or it may have the structure of a plurality of layers each ofwhich is formed of the same material or different materials.

The metal complex of 8-quinolinol derivative can be used as a materialfor the light-emitting layer and as a material for theelectron-injecting layer as described above. Specific examples of themetal complex of 8-quinolinol derivative includetris(8-quinolinol)aluminum, bis(8-quinolinol)magnesium,bis(benzo-8-quinolinol)zinc, bis(2-methyl-8-quinolate aluminum oxide,tris (8-quinolinol) indium, tris(5-methyl-8-quinolinol)aluminum,8-quinolinollithium, tris(5-chloro-8-quinolinol)gallium,bis(5-chloro-8-quinolinol)calcium,tris(5,7-dichloro-8-quinolinol)aluminum,tris(5,7-dibromo-8-hydroxyquinolinol)aluminum,bis(8-quinolinol)beryllium, bis(2-methyl-8-quinolinol)beryllium,bis(8-quinolinol) zinc, bis(2-methyl-8-quinolinol)zinc,bis(8-quinolinol)tin, and tris(7-propyl-8-quinolinol)aluminum.

Specific examples of the material for the protective layer include acopolymer obtained by copolymerizing a monomer mixture containingtetrafluoroethylene and at least one comonomer, a fluorine-containingcopolymer of which the copolymer main chain contains a cyclic structure,polyethylene, polypropylene, polymethyl methacrylate, polyimide,polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene,polydichlorodifluoroethylene, a copolymer from chlorotrifluoroethyleneand dichlorodifluoroethylene, a water-absorption substance having awater absoprtion ratio of at least 1%, a humidity-preventive substancehaving a water absorption ratio of 0.1% or less, metals such as In, Sn,Pb, Au, Cu, Ag, Al, Ti and Ni, metal oxides such as MgO, SiO, SiO₂, Al₂O₃, GeO, NiO, CaO, BaO, Fe₂ O₃, Y₂ O₃ and TiO₂, and metal fluorides suchas MgF₂, LiF, AlF₃ and CaF₂.

Further, the methods of forming the layers (including the anode and thecathode) which constitute the organic EL device as an encapsulatingobject are not specially limited. As methods of forming the anode, thecathode, the light-emitting layer, the hole-transporting layer and theelectron-injecting layer, for example, a vacuum deposition method, aspin coating method, a casting method, a sputtering method and an LBmethod may be applied. For forming the light-emitting layer, however, itis preferred to apply any method (a vacuum deposition method, a spincoating method, a casting method or an LB method) other than thesputtering method. The light-emitting layer is particularly preferably amolecule-deposited film. The term "molecule-deposited film" refers to athin film formed by deposition from a material compound in a gaseousstate or a film formed by solidifying a material compound which is in asolution or liquid state. Generally, the above molecule-deposited filmis distinguishable from a thin film formed by an LB method(molecule-accumulated film) on the basis of differences in cohesivestructure and high-order structure and functional differences caused bythem. When the light-emitting layer is formed by a spin coating method,a coating solution is prepared by dissolving a binder such as a resinand a material compound in a solvent.

The protective layer can be formed by any one of a vacuum depositionmethod, a spin coating method, a sputtering method, a casting method, anMBE (molecular beam epitaxy) method, a cluster ion beam method, an ionplating method, a plasma polymerization method (high-frequency exitedion plating method), a reactive sputtering method, a plasma CVD method,a laser CVD method, a heat CVD method and a gas source CVD method.

The method of forming each layer can be changed as required dependingupon materials used. When the vacuum deposition method is used forforming each layer which constitutes the organic EL device, the organicEL device can be formed by the vacuum deposition method alone, which isadvantageous for simplifying facilities and decreasing the productiontime.

In the encapsulated organic EL device of the present invention, obtainedby providing the above inert liquid layer on the periphery of an organicEL device as an encapsulating object, the presence of the inert liquidlayer firmly prevents the occurrence of a dark spot and the growth of adark spot, and the device therefore has a longer life.

The present invention will be further explained by contrasting Examplesand Comparative Examples hereinafter, while the present invention shallnot be limited to the following Examples. The method of preparingorganic EL devices used as encapsulating objects in Examples andComparative Examples will be explained first.

When an organic EL device as an encapsulating object was produced, atransparent substrate obtained by forming an ITO film having a thicknessof 100 nm on a 25 mm×75 mm×1.1 mm glass substrate was provided first.The substrate was measured for a light transmittance with UV-3100PCsupplied by Shimadzu Corporation, to show about 80% in a wavelengthregion of 400 to 600 nm. The substrate was ultrasonically washed inisopropyl alcohol for 5 minutes and in pure water for 5 minutes, and thewashed substrate was further UV-ozone-cleaned with an apparatus suppliedby SAMCO International Laboratories.

Then, the substrate was fixed to a substrate holder in a commerciallyavailable vapor deposition apparatus (supplied by ULVAC Japan, Ltd.),and 200 mg of N,N'-bis(3-methylphenyl-N,N'-diphenyl1,1'-biphenyl!-4,4'-diamine (to be abbreviated as "TPD" hereinafter) wasplaced in a resistance heating boat formed of molybdenum. Further, 200mg of 4,4'-bis(2,2'-diphenylvinyl)biphenyl (to be abbreviated as "DPVBi"hereinafter) was placed in another resistance heating boat formed ofmolybdenum, and then the vacuum chamber was pressure-decreased to 1×10⁻⁴Pa.

Then, the boat with TPD in it was heated to 215 to 220° C. to depositTPD on the above ITO film at a deposition rate of 0.1 to 0.3 nm/s and toform a hole-transporting layer having a thickness of 60 nm. In thiscase, the substrate had a temperature of room temperature. While theabove-obtained product was allowed to remain in the vacuum chamber afterthe formation of the hole-transporting layer, the above-the boat withDPVBi in it was heated up to 240° C. to deposit DPVBi on thehole-transporting layer at a deposition rate of 0.1 to 0.3 nm/s to forma light-emitting layer having a thickness of 40 nm. In this case, thesubstrate also had a temperature of room temperature.

The above-obtained product was taken out of the vacuum chamber, a maskformed of stainless steel was placed on the above light-emitting layer,and the resultant set was again fixed to the substrate holder. Then, 200mg of tris(8-quinolinol)aluminum (to be abbreviated as "Alq₃ "hereinafter) was placed in one boat formed of molybdenum, and 1 g of amagnesium ribbon was placed in the other boat formed of molybdenum.Further, 500 mg of a silver wire was placed in a basket formed oftungsten, and these boats were set in the vacuum chamber.

Then, the vacuum chamber was pressure-decreased to 1×10⁻⁴ Pa, andthereafter, the boat with Alq₃ in it was heated up to 230° C. to depositAlq₃ on the above light-emitting layer at a deposition rate of 0.01 to0.03 nm/s and to form an electron-injecting layer having a thickness of20 nm. Further, the silver was deposited on the above electron-injectinglayer at a deposition rate of 0.1 nm/s, and at the same time, themagnesium was deposited on the above electron-injecting layer at adeposition rate of 1.4 nm/s, to form an opposite electrode having athickness of 150 nm and being formed of mixed metals of magnesium andsilver. The opposite electrode was measured for a reflectance withUV-3100PC supplied by Shimadzu Corporation to show 80% in the wavelengthregion of 400 to 600 nm.

The opposite electrode was finally formed as described above, to give anorganic EL device as an encapsulating object. The organic EL device wasa device in which an ITO film as an anode, a TPD layer as ahole-transporting layer, a DPVBi layer as a light-emitting layer, anAlq₃ layer as an electron-injecting layer and a layer ofmagnesium-silver mixed metals as an opposite electrode (cathode) wereconsecutively laminated on one main surface of the glass substrate. Partof the ITO film and part of the layer of magnesium-silver mixed metalsworked as lead wires from the electrodes, and the light-emitting layerhad a size of 6 mm×10 mm when viewed as a flat surface.

EXAMPLE 1

(1) Preparation of inert liquid having a dissolved oxygen concentrationof 1 ppm or less

As an inert liquid of which the dissolved oxygen concentration was notadjusted, there was provided perfluoropolyether (Demnum S-20 (tradename; vapor pressure at 25° C., 10⁻⁶ Torr; kinetic viscosity at 25° C.,53 cSt), supplied by Daikin Industries Ltd.) . A proper amount of theabove DemnumS-20 was placed in a glass sample container with a vacuumvalve, and the sample container and a vacuum pump with a diffusion pump(ULVAC VPC-050, supplied by ULVAC Japan, Ltd.) were connected to eachother with a flange.

Then, a zeolite formed of polytetrafluoroethylene (Teflon) was insertedinto the Demnum S-20 in the above sample container, and while the Demnumwas stirred at room temperature, the sample container was vacuumed to10⁻⁴ Torr to exhaust dissolved oxygen by a ordinary temperature vacuumdegassing method for about 30 minutes until no foaming was found.

The above-prepared inert liquid had a dissolved oxygen concentration of0.05 ppm and a water content of 5 ppm. The dissolved oxygenconcentration was measured with SUD-1 (trade name of a measuringapparatus) supplied by Central Kagaku, Ltd. In a gloved box in which theatmosphere was purged with nitrogen gas, the inert liquid was floweddown a sensor portion of the above apparatus at a constant flow rate of50 ml/minute, and when displayed values were stabilized after about 20seconds, the measurement value was read. Further, the inert liquid wasmeasured for a water content by a Karl Fischer's titration method.

(2) Encapsulation

First, there was provided a cap-shaped housing material formed of glass(counterbored substrate supplied by Howa Industries). The housingmaterial had one concave portion having an inner dimension of 13 mm×13mm×1 mm and had an outer dimension of 15 mm×15 mm×18 mm. Further, aninlet for charging the inert liquid was formed in the bottom of theconcave portion of the housing material.

Then, the glass substrate on which the above organic EL device wasformed and the above housing material were bonded to each other with anepoxy resin adhesive (ARALDITE AR-R30, supplied by Ciba Geigy) such thatthe organic EL device as an encapsulating object was placed within theabove concave portion. In this case, the organic EL device was presentin a space formed by the concave portion of the housing material and thesubstrate, and the organic EL device and the housing material were outof contact.

The resultant set was allowed to stand for 3 hours to cure the adhesive,and then the set was vacuum-dried with a vacuum desiccator. Thevacuum-dried set was transferred into a gloved box in which theatmosphere was purged with nitrogen gas, and in the gloved box, theinert liquid prepared in the above (1) was charged into the space formedby the concave portion of the housing material and the substrate throughthe inlet formed in the housing material. In the gloved box, after thecharging of the inert liquid, the above inlet was closed with an epoxyresin adhesive (ARALDITE AR-R30, supplied by Ciba Geigy), and the setwas allowed to stand in the gloved box for about 3 hours until theadhesive was cured.

An inert liquid layer was formed on the periphery of the organic ELdevice as an encapsulating object by charging the inert liquid preparedin the above (1) into the space formed by the concave portion of thehousing material and the substrate, whereby the encapsulating as anobject was performed. At the same time, an encapsulated organic ELdevice as an object was obtained. FIG. 1 shows a schematic crosssectional view of the encapsulated organic EL device.

As shown in FIG. 1, the above-obtained encapsulated organic EL device 1of the present invention has an inert liquid layer 20 of the inertliquid prepared in the above (1) formed on the periphery of an organicEL device 10 as an encapsulating object. The organic EL device 10 as anencapsulating object is formed by consecutively laminating an ITO film12 as an anode, a TPD layer 13 as a hole-transporting layer, a DPVBilayer 14 as a light-emitting layer, an Alq₃ layer as anelectron-injecting layer and a layer 16 of magnesium-silver mixed metalsas an opposite electrode (cathode) on the a glass substrate 11. Part 12aof the ITO film 12 and part 16a of the layer 16 of magnesium-silvermixed metals constitute lead wires from the electrodes. The organic ELdevice 10 is present in a space formed by the concave portion of thehousing material 18 fixed onto the glass substrate 11 with an epoxyresin adhesive 17 and the glass substrate 11, and the space was chargedwith the inert liquid prepared in the above (1). As a result, the inertliquid layer 20 is formed on the periphery of the organic EL device 10.The inert liquid is a liquid charged through an inlet 19 provided in thehousing material 18, and the inlet 19 is closed with an epoxy resinadhesive 17a after the charging of the inert liquid.

(3) Evaluation of encapsulating effect

The encapsulated organic EL device obtained in the above (2) wasconnected to a direct-current constant-current electric source throughthe two lead wires of the organic EL device, and electricity was appliedsuch that an initial brightness at 25° C. in the atmosphere was 100cd/m². In this case, the current value was 0.56 mA, and the voltagevalue was 9 V. The brightness was measured with a luminance meter (tradename CS-100) supplied by Minolta Camera Cc., Ltd.

After the above electric application, an enlarged photograph of thelight-emitting surface was taken (magnification, 10 times), and a ratioof the total area of dark spots viewed as a flat surface to the area ofthe light-emitting surface viewed as a flat surface (to be referred toas "no-light emission area ratio" hereinafter) was determined on thebasis of the above photograph, to obtain 0.43%. Further, one dark spotwas measured for a diameter to show 18.4 μm.

Further, 139 hours after the electric application was initiated, ano-light emission area ratio was determined in the same manner as above,and the same dark spot as that measured above was measured for adiameter. Further, the growth ratio of a dark spot was defined to be adiameter increment value per hour, and the value thereof was determined.Table 2 shows the results.

EXAMPLE 2

Ordinary temperature vacuum degassing was carried out under the sameconditions as those in Example 1 (1) except that the inert liquid ofwhich the dissolved oxygen concentration was not adjusted was replacedwith perfluoropolyether (Fomblin Z03 (trade name; vapor pressure at 25°C., 10⁻⁴ Torr; kinetic viscosity at 25° C., 30 cSt) , supplied byMontecatini), to prepare a inert liquid having a dissolved oxygenconcentration of 0.1 ppm and a water content of 5 ppm. Then, anencapsulating as an object was carried out under the same conditions asthose in Example 1 except that the inert liquid used for forming aninert liquid layer on the periphery of an organic EL device was replacedwith the above-prepared inert liquid. At the same time, an encapsulatedorganic EL device as an object was also obtained.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 1(3) except that the secondcalculation or measurement of a no-light emission area and a dark spDtdiameter was conducted 152 hours after the initiation of electricapplication. Table 2 shows the results.

Comparative Example 1

Ordinary temperature vacuum degassing was carried out under the sameconditions as those in Example 1 (1) except that the inert liquid ofwhich the dissolved oxygen concentration was not adjusted was replacedwith perfluoroamine (Fluorinert FC-70 (trade name; vapor pressure at 25°C., 0.1 Torr , supplied by Sumitomo-3M Co., Ltd.). However, thedegassing was not fully performed since the above inert liquid had ahigher vapor pressure than 10⁻² Torr at 25° C., and the prepared inertliquid had a dissolved oxygen concentration of 2 ppm or outside therange limited in the present invention. Further, the inert liquid had awater content of 20 ppm. Further, an organic EL device was encapsulatedunder the same conditions as those in Example 1 except that the inertliquid used for forming an inert liquid layer on the periphery of theorganic EL device was replaced with the above inert liquid, to give anencapsulated organic EL device.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 1 (3) except that the secondcalculation or measurement of a no-light emission area and a dark spotdiameter was conducted 124 hours after the initiation of electricapplication. Table 2 shows the results.

Comparative Example 2

Ordinary temperature vacuum degassing was carried out under the sameconditions as those in Example 1(1) except that the inert liquid ofwhich the dissolved oxygen concentration was not adjusted was replacedwith perfluoroamine (Fluorinert FC-43 (trade name; vapor pressure at 25°C., 1.3 Torr , supplied by Sumitomo-3M Co., Ltd.). However, thedegassing was not fully performed since the above inert liquid had ahigher vapor pressure than 10⁻² Torr at 25° C., and the prepared inertliquid had a dissolved oxygen concentration of 10 ppm or outside therange limited in the present invention. Further, the inert liquid had awater content of 50 ppm. Further, an organic EL device was encapsulatedunder the same conditions as those in Example 1 except that the inertliquid used for forming an inert liquid layer on the periphery of theorganic EL device was replaced with the above inert liquid, to give anencapsulated organic EL device.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 1(3) except that the secondcalculation or measurement of a no-light emission area and a dark spotdiameter was conducted 136 hours after the initiation of electricapplication. Table 2 shows the results.

Comparative Example 3

An organic EL device was encapsulated under the same conditions as thosein Example 1 except that an organic EL device as an encapsulating objectwas encapsulated under the same conditions as those in Example 1 exceptthat the perfluoropolyether (Demnum S-20 (trade name), supplied byDaikin Industries Ltd.) which was vacuum-degassed in Example 1 wasreplaced with an inert liquid which was perfluoropolyether (Demnum S-20(trade name), supplied by Daikin Industries Ltd.) not vacuum-degassed,to give an encapsulated organic EL device. The above inert liquid had adissolved oxygen concentration of 8.0 ppm, or outside the range limitedin the present invention.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 1(3) except that the secondcalculation or measurement of a no-light emission area and a dark spotdiameter was conducted 115 hours after the initiation of electricapplication. Tab le 2 shows the results.

                  TABLE 2    ______________________________________    No-light emission                     Diameter of dark    area ratio (%)   spot (μm)               After pre-        After pre-                                         Growth               determined        determined                                         rate of               period of         period of                                         dark spot    Initial    time      Initial time    (μm/hour)    ______________________________________    Ex. 1  0.43    0.51      18.4  20.1    1.22 × 10.sup.-2    Ex. 2  0.43    0.59      18.4  19.1    4.61 × 10.sup.-3    CEx. 1 0.45    3.9       18.3  45.7    2.21 × 10.sup.-1    CEx. 2 0.42    12.3      18.5  121.9   7.60 × 10.sup.-1    CEx. 3 0.46    12.4      18.8  82.5    5.55 × 10.sup.-1    ______________________________________     Ex. = Example, CEx. = Comparative Example     *: "After predetermined period of time" in Example 1 stands for 139 hours     after the electric application, "After predetermined period of time" in     Example 2 stands for 152 hours after the electric application, "After     predetermined period of time" in Comparative Example 1 stands for 124     hours after the electric application, "After predetermined period of time     in Comparative Example 2 stands for 136 hours after the electric     application, and "After predetermined period of time" in Comparative     Example 3 stands for 115 hours after the electric application.

As is shown in Table 2, the encapsulated organic EL devices obtained inExamples 1 and 2 showed almost no changes from initial values in theno-light emission area ratio and the diameter of a dark spot 139 hoursor 152 hours after the electric application, and the growth rate of adark spot in each was also low. These data show that each of the inertliquid layers formed in Examples 1 and 2 firmly prevented the growth ofdark spots.

In contrast, in the encapsulated organic EL devices obtained inComparative Examples 1 to 3, the no-light emission ratios and thediameters of dark spots were greatly larger than their initial valuesafter predetermined periods of time passed after the electricapplication, and the growth ratio in each Comparative Example was muchlarger than those ratios in Examples 1 and 2.

EXAMPLE 3

(1) Preparation of inert liquid having a dissolved oxygen concentrationof 1 ppm or less

An inert liquid having a dissolved oxygen concentration of 0.05 ppm anda water content of 5 ppm was prepared in the same manner as in Example1(1).

(2) Activation treatment of adsorbent

Activated alumina (supplied by Hiroshima Wako Purechemical IndustriesLtd.; particle diameter about 300 mesh) was provided as an adsorbent. Aproper amount of the activated alumina was placed in a glass samplecontainer with a vacuum valve, and the sample container and a vacuumpump were connected to each other with a flange.

Then, the above sample container was vacuumed to 10⁻⁴ Torr at roomtemperature, and while the portion retaining the activated alumina inthe above sample container was heated at 280° C. with a heater, thesample container was further vacuumed. The above vacuuming was continuedfor 5 hours until the generation of gas from the activated alumina wasnot found so that a vacuum degree was stabilized, and then the vacuumvalve was closed for storage.

(3) Encapsulation

The same cap-shaped housing material as the cap-shaped housing materialused in Example 1(2) was provided. The housing material and an organicEL device were bonded to each other in the same manner as in Example1(2), and then the resultant set was vacuum-dried with a vacuumdesiccator. The vacuum-dried set was transferred into a gloved box inwhich the atmosphere was purged with nitrogen gas.

Further, the above sample container containing the inert liquid preparedin the above (1) and the above sample container containing the adsorbentactivation-treated in the above (2) were transferred into the abovegloved box. Then, a predetermined amount of the adsorbent was chargedinto the sample container containing the inert liquid, and the mixturewas stirred to prepare an inert liquid containing the adsorbent (to bereferred to as "mixture liquid" hereinafter). The mixture liquidcontained 500 mg of the adsorbent permilliliter of the inert liquid, andthe mixture liquid had a dissolved oxygen concentration of 1 ppm orless. Thereafter, the mixture liquid was charged into a space formed bythe concave portion of the housing material and the substrate through aninlet provided in the above housing material.

After the charging of the mixture liquid, in the above gloved box, theabove inlet was closed with an epoxy resin adhesive (ARALDITE AR-R30,supplied by Ciba Geigy), and the set was allowed to stand in the glovedbox for about 3 hours until the adhesive was cured.

An inert liquid layer was formed on the periphery of the organic ELdevice as an encapsulating object by charging the above mixture liquidinto the space formed by the concave portion of the housing material andthe substrate, whereby the encapsulating as an object was performed. Atthe same time, an encapsulated organic EL device as an object wasobtained. FIG. 2 shows a schematic cross sectional view of theencapsulated organic EL device.

As shown in FIG. 2, the above-obtained encapsulated organic EL device 30has an inert liquid layer 31 formed on the periphery of an organic ELdevice 10 as an encapsulating object, the inert liquid layer 31 beingformed of mixture liquid (inert liquid containing adsorbent) consistingof an inert liquid 31a prepared in the above (1) and an adsorbent 31bactivation-treated in the above (2). In the encapsulated organic ELdevice shown in FIG. 2, the same members as those in FIG. 1 are shown bythe same reference numerals, and explanations thereof are omitted.

(4) Evaluation of encapsulating effects

The encapsulated organic EL device obtained in the above (3) wasevaluated for encapsulating effects in the same manner as in Example1(3) except that the calculation of a no-light emission area ratio andthe measurement of a dark spot diameter were conducted 5 days and 30days after the initiation of electric application. Table 3 shows theresults.

EXAMPLE 4

An Mg powder (supplied by Kojundo Chemical Laboratory Co., Ltd.;particle diameter 80 mesh or less) was provided as an adsorbent, and theMg powder was activation-treated as follows.

First, a proper amount of the Mg powder was placed in a beaker, and a 1Mhydrochloric acid aqueous solution was added. The mixture was allowed tostand for several minutes, and then filtered, and the residue (Mgpowder) was rinsed with a sufficient amount of anhydrous ethanol. Therinsed residue (Mg powder) was transferred to a glass sample containerwith a vacuum valve, and the valve of the sample container was closed.The procedures so far were carried out in a gloved box in which drynitrogen gas had been blown. The above sample container (containing theresidue (Mg powder)) of which the valve was closed was taken out of thegloved box, and the Mg powder in the container was subjected tovacuuming in the same manner as in Example 1 until the evaporation ofethanol was not found so that the vacuum degree was stabilized. Theabove vacuuming was carried out at room temperature without heating aportion retaining the Mg powder in the above sample container.

An organic EL device was encapsulated in the same manner as in Example 3except that the adsorbent was replaced with the Mg powder which wasactivation-treated as described above, and at the same time, anencapsulated organic EL device was obtained. In this case, the inertliquid layer contained 500 mg of the adsorbent per milliliter of theinert liquid, and had a dissolved oxygen concentration of 1 ppm or less.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 3(4). Table 3 shows theresults. Example 5 An organic EL device was encapsulated in the samemanner as in Example 3 except that the adsorbent was replaced with apowder (particle diameter 300 mesh or less) of CaSO₄.1/2H₂ O (calcinedgypsum; supplied by Wako Purechemical Industries Ltd.), that the heatingtemperature by a heater for the activation treatment of the adsorbentwas changed to 240° C. and that the mixture liquid was replaced with amixture liquid (inert liquid containing the inert liquid) containing 200mg of the adsorbent per milliliter of the inert liquid, and at the sametime, an encapsulated organic EL device was obtained. In this case, theinert liquid layer had a dissolved oxygen concentration of 1 ppm orless.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 3(4). Table 2 shows theresults.

Referential Example 1

An organic EL device was encapsulated in the same manner as in Example 3except that no adsorbent was used. The encapsulated organic EL devicewas evaluated for encapsulating effects in the same manner as in Example3(4). Table 3 shows the results.

Comparative Example 4

An organic EL device was encapsulated in the same manner as in Example 3except that perfluoropolyether (Demnum S-20 (trade name), supplied byDaikin Industries Ltd.) was used as an inert liquid withoutvacuum-degassing it.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 3(4). Table 3 shows theresults.

Comparative Example 5

An organic EL device was encapsulated in the same manner as in Example 3except that activated alumina (particle diameter about 300 mesh,supplied by Hiroshima Wako Purechemical Industries Ltd.) was exposed toatmosphere and then used as an adsorbent without activating--treatingit. The mixture liquid (inert liquid containing the adsorbent) used forforming an inert liquid layer had a dissolved oxygen concentration of5.0 ppm or outside the range limited in the present invention, sinceoxygen adsorbed on the adsorbent was dissolved in the inert liquid.

The above encapsulated organic EL device was evaluated for encapsulatingeffects in the same manner as in Example 3(4). Table 3 shows theresults.

                  TABLE 3    ______________________________________    No-light emission   Diameter of    area ratio (%)      dark spot (μm)               After 5 After 30       After 5                                            After 30    Initial    days    days     Initial                                      days  days    ______________________________________    Ex. 3  0.20    0.20    0.25   15    15    17    Ex. 4  0.20    0.20    0.25   15    15    17    Ex. 5  0.20    0.20    0.25   15    15    17    REx. 1 0.20    0.25    12     15    17    80    CEx. 4 0.20    4.0     50     15    50    300    CEx. 5 0.20    4.0     50     15    50    300    ______________________________________     Ex. = Example, REx. = Referential Example, CEx. = Comparative Example

As shown in Table 3, in the encapsulated organic EL devices obtained inExamples 3 to 5, the increase of the no-light emission area ratio withthe passage of time and the growth of dark spots with the passage oftime were firmly prevented.

On the other hand, in the encapsulated organic EL device obtained inReferential Example 1, the increase of the no-light emission area ratiowith the passage of time and the growth of dark spots with the passageof time were firmly prevented as compared with the data of theencapsulated organic EL devices obtained in Comparative Examples 4 and5, while the encapsulating effects were low as compared with the data ofthe encapsulated organic EL devices obtained in Examples 3 to 5.

Further, in the encapsulated organic EL device obtained in ComparativeExample 4, the no-light emission area ratio immensely increased with thepassage of time and dark spots immensely grew with the passage of time,and the encapsulating effects were low. In Comparative Example 5 inwhich the adsorbent was exposed to atmosphere and then used withoutactivation treatment, to form the inert liquid layer having a dissolvedoxygen concentration of 5.0 ppm, the no-light emission area ratioimmensely increased with the passage of time, and dark spots immenselygrew with the passage of time, similarly to the encapsulated organic ELdevice obtained in Comparative Example 4, and no effect of the use ofthe adsorbent was found.

As explained above, the method Df the present invention can firmlyprevent the growth of dark spots in an organic EL device. The working ofthe present invention therefore can provide organic EL devices having anincreased device life.

We claim:
 1. A method of encapsulating an organic electroluminescencedevice, which comprises providing a layer of an inert liquid having adissolved oxygen concentration of 1 ppm or less on the periphery of anorganic electroluminescence device, the electroluminescence device beingformed by laminating an anode and a cathode through at least alight-emitting layer.
 2. The method of claim 1, wherein the inert liquidhas a water content of 10 ppm or less.
 3. The method of claim 1, whereinthe inert liquid inert liquid is a liquid fluorinated carbon having avapor pressure of 10⁻² Torr or less at 25° C.
 4. The method of claim 1,which further comprises providing a housing material which covers theorganic electroluminescence device, said electroluminescence devicebeing formed on a substrate, which forms a space between the organicelectroluminescence device and the housing material, and filling theinert liquid having a dissolved oxygen concentration of 1 ppm or less insaid space.
 5. The method of claim 1, wherein the inert liquid is aninert liquid containing an adsorbent.
 6. The method of claim 5, whereinthe adsorbent is selected from the group consisting of(a) an inorganiccompound selected from the group consisting of activated alumina,diatomaceous earth, activated carbon, hemihydrated gypsum, phosphoruspentoxide, magnesium perchlorate, potassium hydroxide, calcium sulfate,calcium bromide, calcium oxide, zinc chloride, zinc bromide andanhydrous copper sulfate, (b) a metal selected from the group consistingof lithium, beryllium, potassium, sodium, magnesium, rubidium, strontiumand calcium, or an alloy thereof, and (c) an acrylic water-absorptionpolymer or a methacrylic water-absorption polymer.
 7. The method ofclaim 5, wherein the adsorbent is an adsorbent which isactivation-treated.
 8. The method of claim 5, wherein the inert liquidcontains 1 mg to 10 g of the adsorbent per milliliter of the inertliquid.
 9. The method of claim 5, wherein the inert liquid is an inertliquid having a water content of 10 ppm or less.
 10. The method of claim5, wherein the inert liquid is a liquid fluorinated carbon having avapor pressure of 10⁻² Torr or less at 25° C.
 11. The method of claim 5,wherein the layer of the inert liquid containing the adsorbent is formedby providing a housing material which covers the organicelectroluminescence device, said electroluminescence device being formedon a substrate, which forms a space between the organicelectroluminescence device and the housing material, and filling theinert liquid in said space.
 12. The method of claim 1, wherein thedissolved oxygen concentration is 0.01 to 1 ppm.
 13. An encapsulatedorganic electroluminescence device comprising an organic device formedby laminating an anode and a cathode through at least a light-emittinglayer, and a layer of an inert liquid which is provided on the peripheryof the organic electroluminescence device, the layer of the inert liquidhaving a dissolved oxygen concentration of 1 ppm or less.
 14. Theencapsulated organic electroluminescence device of claim 13, wherein theinert liquid has a water content of 10 ppm or less.
 15. The encapsulatedorganic electroluminescence device of claim 13, wherein the inert liquidis a liquid fluorinated carbon having a vapor pressure of 10⁻² Torr orless at 25° C.
 16. The encapsulated organic electroluminescence deviceof claim 13, wherein the layer of the inert liquid is formed of an inertliquid containing an adsorbent.
 17. The encapsulated organicelectroluminescence device of claim 16, wherein the adsorbent isselected from the group consisting of(a) an inorganic compound selectedfrom the group consisting of activated alumina, diatomaceous earth,activated carbon, hemihydrated gypsum, phosphorus pentoxide, magnesiumperchlorate, potassium hydroxide, calcium sulfate, calcium bromide,calcium oxide, zinc chloride, zinc bromide and anhydrous copper sulfate,(b) a metal selected from the group consisting of lithium, beryllium,potassium, sodium, magnesium, rubidium, strontium and calcium, or analloy thereof, and (c) an acrylic water-absorption polymer or amethacrylic water-absorption polymer.
 18. The encapsulated organicelectroluminescence device of claim 16, wherein the adsorbent is anactivation-treated adsorbent.
 19. The encapsulated organicelectroluminescence device of claim 16 wherein the inert liquid contains1 mg to 10 g of the adsorbent per milliliter of the inert liquid. 20.The encapsulated organic electroluminescence device of claim 13 whereinthe organic electroluminescence device is formed on a substrate, andwhich further comprises a housing material which covers the organicelectroluminescence device formed on the substrate, which forms a spacebetween the organic electroluminescence device and the housing material,and the layer of the inert liquid is formed in said space.